Cook County Assessor Publishes 20 Years of Historic Assessment Data

Wednesday, June 8, 2022

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Millions of data points available to property owners, researchers, and journalists

Cook County – Affirming his commitment to government transparency, Cook County Assessor Fritz Kaegi recently published millions of rows of data on Cook County’s Open Data Portal.
Datasets from the Cook County Assessor’s Office can be viewed and downloaded online at The data for each property contains the following. 

  • Assessed values from 1999 to 2021
  • Transaction/sales data
  • Location data, such as which school districts the property is in, and distances to amenities like the nearest L station or the lakefront
  • Characteristics of homes and condos in Cook County

“Since the start of my administration, I’ve prioritized transparency and data integrity. The publication of this historic assessment data demonstrates my dedication to these values,” said Assessor Fritz Kaegi. “I encourage the public to view this informative data to learn more about their community.”

The datasets are published on Cook County’s Open Data Portal, where users can filter by Property Index Number (PIN), export information, create visualizations, and connect to the data using an API. These datasets will automatically update periodically with new information as it is entered into iasWorld, the Assessor’s Office’s modernized assessment system of record.

Previously published public data from the Assessor’s Office includes the valuation model available on Gitlab, valuation reports for reassessed townships, and, most recently, the Chicago reassessment data dashboard.

To promote the release of 20 years of assessment information, the Data team of the Cook County Assessor’s Office will host an “Ask Me Anything” session on Reddit on Thursday, June 9 at 4 pm. The team will answer questions about these datasets, Chicago’s 2021 reassessment, the CCAO’s reassessment models, and more.

Ask your questions at:

Cook County Assessor’s Office Data team on Reddit: 

Cook County Assessor’s Office on the County Open Data Portal: 

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